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Always On availability groups (AGs) provide a replicated environment for one or more SQL Server databases. Databases that need to failover together are placed in the same AG. When using Availability Groups, the main database or databases are known as the ‘primary’ and data is replicated to one or more copies known as ‘secondaries’. An important distinction between FCI and AG is that FCI protects an entire SQL Server instance and all the databases it contains. By contrast, AGs are configured at the database level and protect a single database or a group of databases. Another important difference is that shared storage used with FCI, and storage for AGs are agnostic. Because AG uses separate compute and storage, it is sometimes referred to as a shared nothing architecture. Availability groups can be deployed on all supported platforms such as Windows, Linux, containers, and Kubernetes. SQL Server FCIs can be used as the basis for AGs to provide an additional layer of resiliency. For complete information, see the Microsoft article What is an Always On availability group.